Implantable medical devices including those that are positioned on the exterior of a body of a patient as well as those that are positioned subcutaneously or deeper typically utilize an on-board battery that allows the patient to be untethered to a power source. The patient maintains mobility while the implantable medical device performs a particular medical task by operating on power from the battery. For instance, the implantable medical device may provide stimulation therapy for neurological or cardiac conditions, may provide drug delivery for various conditions such as pain management, and/or may provide physiological monitoring.
While the on-board battery may power the medical device for a relatively long period of time, the on-board battery will eventually be depleted. Prior to rechargeable medical systems, the implantable medical device would be replaced once the battery became depleted. With rechargeable medical systems, an external device provides recharge energy over a proximity coupling, which is typically inductive, to the implantable medical device. This recharge energy restores the on-board battery to a satisfactory level for continued operation of the medical device.
During a recharge session, the external device in control of the recharge energy and the implantable medical device to be recharged exchange telemetry communications related to the recharge process. Recharge information such as battery status, coupling efficiency and the like may be transferred in this manner so that the external device can properly control delivery of the recharge energy as well as instruct a user. Conventionally, the two devices exchange telemetry communications over a proximity coupling. However, far field telemetry communications using radio frequency communications such as those in the Medical Implant Communication Service (MICS) band allow for far field telemetry communications between the external device and the implantable medical device.
While far field telemetry communications may be employed during a recharge session for one or more reasons, such as to provide convenience to the users and/or to increase the efficiency of the recharge process by using a proximity coupling only for recharge energy delivery, issues may also arise. Because far field telemetry communications are capable of extending to other external devices and implantable devices in the vicinity, far field telemetry communications typically call for a pairing to exist between devices in the form of a bond, where that bond may be implemented as knowledge of an identifier of the other device and/or a shared encryption key. For systems where a prior bond is necessary to establish a recharge session, if one of the two devices involved in an attempted recharge session is already paired with another device, then the recharge attempt may present additional issues, such as a failure of the recharge session to commence, failure to communication recharge information over far field telemetry communications, and so forth. Examples of situations where this may arise include the case of one user's patient therapy module attempting to recharge another user's implantable medical device, an external device of a sales representative or clinician attempting to recharge a patient's implant, and so forth.